1. Field of the Invention
The invention relates to the precision control of operate and release times for relays.
2. Description of the Prior Art
The invention was developed for the system shown in U.S. Pat. No. 3,767,863, issued Oct. 23, 1973, by Borbas et al. for a Communication Switching System with Modular Organization and Bus, hereinafter referred to as the System S2 patent.
Various methods have been used in the past to try to control the operate and release times of relays in order to accomplish various logic and switching requirements. In System S2, one such requirement is controlling the operate and release time of a specific relay (Relay B in sender) in order to close and release the contacts of the switching network when a signal is not being applied to those contacts, and to do so throughout a whole system so that a path has been formed before a signal is applied. One method used previously was to put copper slugs on certain types of relays (Class B) in order to obtain the slow to operate or slow to release relay. A second method involved using electrolytic capacitors and resistors in cooperation with the relays to provide the desired delays. These two methods produced delays which were not of sufficient accuracy for the System S2.
A third method was the combination of a unijunction transistor and SCR device. This method, although fairly accurate, presents a high circuit cost. All three of these methods were adaptable to provide only a specific operate time or a specific release time. In those particular methods to provide both a specific operate and a specific release time was extremely difficult.